The present invention relates to materials deposition, particularly to a method for reducing material waste during deposition processing, and more particular to a method for material deposition by ablation transfer processing using a patterned, pulsed, high intensity energy beam to achieve both deposition and patterning.
Numerous manufacturing processes have been developed for the deposition of semiconducting, insulating or metallic materials. Such processes are generally carried out in a vacuum, utilize so-called high temperature, and thus expensive substrates, and involve substantial waste of the processing material.
Manufacturing processes for active-matrix (AM) substrates used in high-quality liquid crystal flat panel displays, for example, are notorious for their high cost and inefficient use of materials. Typical AM substrates, in which millions of transistors are fabricated in thin films of silicon deposited on glass, have an active silicon area of approximately one percent. However, to build the thin-film-transistors (TFT's), silicon and other necessary materials are deposited over 100 percent of the display. Thus, 99 percent of the deposited materials are wasted. As important, removal of the excess material requires expensive techniques, including lithography and etching steps, which can also contribute significantly to substrate contamination. Thus, a need exists for a more efficient method of manufacturing which would use an additive process in which the silicon, metals, and other materials are deposited only in the regions where they are required. By using such a process, material waste is minimized and etching and lithography are eliminated because the layer configuration or pattern has already been defined during the deposition.
Another problem with the current display manufacturing processes is that high substrate temperatures are required to achieve good material quality in the component layers of the TFT. Typically substrate temperatures exceeding 200.degree. C. for a sustained period of time are utilized. This constrains the choice of substrates to so-called high temperature substrate materials which can withstand any type of deformation at these elevated processing temperatures. In most deposition processes, increased substrate temperature is necessary to impart the depositing atoms with sufficient energy to achieve high quality growth. Unfortunately, this limitation precludes the use of inexpensive, so called low-temperature, flexible plastic or inexpensive glass substrates, which are incapable of withstanding sustained (prolonged) processing temperatures greater than 180.degree.-200.degree. C. Recently, the use of pulsed laser processing has enabled the use of these so-called low-temperature, inexpensive substrates, and such is exemplified by copending U.S. application Ser. No. 08/219,487, filed Mar. 29, 1994, entitled "Electronic Devices Utilizing Pulsed-Energy Crystallized Microcrystalline/Polycrystalline Silicon", J. L. Kaschmitter, et al., and assigned to the same assignee.
A final difficulty inherent to display processing is the need to carry out all depositions in vacuum. This limits throughput during the manufacturing sequence and adds to the cost. The need for vacuum processing arises from the use of toxic gases and/or the need to keep the layers contamination free during the deposition. A method is needed in which the layers are deposited from a solid source at atmospheric pressure, without the use of special vacuum processing equipment and thus further reduce the cost of the manufacturing process.
The present invention solves each of the above-mentioned problems by eliminating unnecessary material waste, enabling the use of inexpensive low-temperature substrates, and being carried out at atmospheric pressure and without the use of vacuum systems. This is accomplished by deposition of materials by ablation transfer processing. Similar in methodology to thermal transfer printing the ablation transfer deposition process of this invention can be used to selectively deposit any type material on almost any type of substrate at room temperature and atmospheric pressure.